The handling of biological fluids must meet severe requirements. In particular the operation of the pump must be free of detrimental effects on the fluid handles or on the man or animal connected to the pump.
These detrimental effects are of several types:
(a) destruction of the formed elements of the blood by shear stress; PA1 (b) induced coagulation; PA1 (c) alteration of the proteins and other biochemical molecules of the fluid.
In centrifugal pumps the last two effects result mainly from heating problems.
Detrimental effects on the patient are embolization of coagulated blood, particles of seals, release or toxic products by the burning of the seal, alteration of circulating proteins. These effects may lead to nonreversible loss of function of the individual.
Prior centrifugal pumps for clinical use are driven indirectly but despite this fact they have frictional bearing seals which have been found to result in significant heat generation and potential degradation of the seals which lead to the detrimental effects referred to above.
Centrifugal pumps for clinical use have a conical shape with an axial suction inlet at the top of the cone and a radial or tangential outlet at the bottom of the pump. The rotator is also conical and comprises blades disposed at regular spaced radii or conical supporting coaxial bell-shaped elements revolving bodily with the rotator. Both types of rotator drive the fluid by viscosity effect.
The conical rotator incorporates a magnetic disc at its base or is solid with a magnetic disc located in a separate chamber, the pumping and magnetic chambers being separated by a partition which also serves as a friction bearing for the axle supporting the rotator. The magnetic chamber is permanently cooled by a continuous flow of cold liquid to ensure cooling of the axle and of the seal and, moreover, this liquid avoids penetration of blood into the magnetic chamber.
In another realization the rotator is rotatably mounted on the base of the housing on a shaft with seals on the housing side and on the rotator side of which the latter is a friction bearing.
In all of these realizations the friction bearings or friction seals not only generate heat but create a hot spot with a temperature high enough to cause blood coagulation. As a result of this none of the prior pumps is suitable for long term use and for intracorporeal implantation. On the other hand, for short term use the general tendency is to use devices for only one procedure so that the high cost of construction of prior pumps is disadvantageous.